services/keep-web/s3.go

   1 // Copyright (C) The Arvados Authors. All rights reserved.
   2 //
   3 // SPDX-License-Identifier: AGPL-3.0
   4
   5 package main
   6
   7 import (
   8         "crypto/hmac"
   9         "crypto/sha256"
  10         "encoding/xml"
  11         "errors"
  12         "fmt"
  13         "hash"
  14         "io"
  15         "net/http"
  16         "net/url"
  17         "os"
  18         "path/filepath"
  19         "sort"
  20         "strconv"
  21         "strings"
  22         "time"
  23
  24         "git.arvados.org/arvados.git/sdk/go/arvados"
  25         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  26         "github.com/AdRoll/goamz/s3"
  27 )
  28
  29 const (
  30         s3MaxKeys       = 1000
  31         s3SignAlgorithm = "AWS4-HMAC-SHA256"
  32         s3MaxClockSkew  = 5 * time.Minute
  33 )
  34
  35 func hmacstring(msg string, key []byte) []byte {
  36         h := hmac.New(sha256.New, key)
  37         io.WriteString(h, msg)
  38         return h.Sum(nil)
  39 }
  40
  41 func hashdigest(h hash.Hash, payload string) string {
  42         io.WriteString(h, payload)
  43         return fmt.Sprintf("%x", h.Sum(nil))
  44 }
  45
  46 // Signing key for given secret key and request attrs.
  47 func s3signatureKey(key, datestamp, regionName, serviceName string) []byte {
  48         return hmacstring("aws4_request",
  49                 hmacstring(serviceName,
  50                         hmacstring(regionName,
  51                                 hmacstring(datestamp, []byte("AWS4"+key)))))
  52 }
  53
  54 // Canonical query string for S3 V4 signature: sorted keys, spaces
  55 // escaped as %20 instead of +, keyvalues joined with &.
  56 func s3querystring(u *url.URL) string {
  57         keys := make([]string, 0, len(u.Query()))
  58         values := make(map[string]string, len(u.Query()))
  59         for k, vs := range u.Query() {
  60                 k = strings.Replace(url.QueryEscape(k), "+", "%20", -1)
  61                 keys = append(keys, k)
  62                 for _, v := range vs {
  63                         v = strings.Replace(url.QueryEscape(v), "+", "%20", -1)
  64                         if values[k] != "" {
  65                                 values[k] += "&"
  66                         }
  67                         values[k] += k + "=" + v
  68                 }
  69         }
  70         sort.Strings(keys)
  71         for i, k := range keys {
  72                 keys[i] = values[k]
  73         }
  74         return strings.Join(keys, "&")
  75 }
  76
  77 func s3stringToSign(alg, scope, signedHeaders string, r *http.Request) (string, error) {
  78         timefmt, timestr := "20060102T150405Z", r.Header.Get("X-Amz-Date")
  79         if timestr == "" {
  80                 timefmt, timestr = time.RFC1123, r.Header.Get("Date")
  81         }
  82         t, err := time.Parse(timefmt, timestr)
  83         if err != nil {
  84                 return "", fmt.Errorf("invalid timestamp %q: %s", timestr, err)
  85         }
  86         if skew := time.Now().Sub(t); skew < -s3MaxClockSkew || skew > s3MaxClockSkew {
  87                 return "", errors.New("exceeded max clock skew")
  88         }
  89
  90         var canonicalHeaders string
  91         for _, h := range strings.Split(signedHeaders, ";") {
  92                 if h == "host" {
  93                         canonicalHeaders += h + ":" + r.Host + "\n"
  94                 } else {
  95                         canonicalHeaders += h + ":" + r.Header.Get(h) + "\n"
  96                 }
  97         }
  98
  99         canonicalRequest := fmt.Sprintf("%s\n%s\n%s\n%s\n%s\n%s", r.Method, r.URL.EscapedPath(), s3querystring(r.URL), canonicalHeaders, signedHeaders, r.Header.Get("X-Amz-Content-Sha256"))
 100         ctxlog.FromContext(r.Context()).Debugf("s3stringToSign: canonicalRequest %s", canonicalRequest)
 101         return fmt.Sprintf("%s\n%s\n%s\n%s", alg, r.Header.Get("X-Amz-Date"), scope, hashdigest(sha256.New(), canonicalRequest)), nil
 102 }
 103
 104 func s3signature(secretKey, scope, signedHeaders, stringToSign string) (string, error) {
 105         // scope is {datestamp}/{region}/{service}/aws4_request
 106         drs := strings.Split(scope, "/")
 107         if len(drs) != 4 {
 108                 return "", fmt.Errorf("invalid scope %q", scope)
 109         }
 110         key := s3signatureKey(secretKey, drs[0], drs[1], drs[2])
 111         return hashdigest(hmac.New(sha256.New, key), stringToSign), nil
 112 }
 113
 114 // checks3signature verifies the given S3 V4 signature and returns the
 115 // Arvados token that corresponds to the given accessKey. An error is
 116 // returned if accessKey is not a valid token UUID or the signature
 117 // does not match.
 118 func (h *handler) checks3signature(r *http.Request) (string, error) {
 119         var key, scope, signedHeaders, signature string
 120         authstring := strings.TrimPrefix(r.Header.Get("Authorization"), s3SignAlgorithm+" ")
 121         for _, cmpt := range strings.Split(authstring, ",") {
 122                 cmpt = strings.TrimSpace(cmpt)
 123                 split := strings.SplitN(cmpt, "=", 2)
 124                 switch {
 125                 case len(split) != 2:
 126                         // (?) ignore
 127                 case split[0] == "Credential":
 128                         keyandscope := strings.SplitN(split[1], "/", 2)
 129                         if len(keyandscope) == 2 {
 130                                 key, scope = keyandscope[0], keyandscope[1]
 131                         }
 132                 case split[0] == "SignedHeaders":
 133                         signedHeaders = split[1]
 134                 case split[0] == "Signature":
 135                         signature = split[1]
 136                 }
 137         }
 138
 139         client := (&arvados.Client{
 140                 APIHost:  h.Config.cluster.Services.Controller.ExternalURL.Host,
 141                 Insecure: h.Config.cluster.TLS.Insecure,
 142         }).WithRequestID(r.Header.Get("X-Request-Id"))
 143         var aca arvados.APIClientAuthorization
 144         var secret string
 145         var err error
 146         if len(key) == 27 && key[5:12] == "-gj3su-" {
 147                 // Access key is the UUID of an Arvados token, secret
 148                 // key is the secret part.
 149                 ctx := arvados.ContextWithAuthorization(r.Context(), "Bearer "+h.Config.cluster.SystemRootToken)
 150                 err = client.RequestAndDecodeContext(ctx, &aca, "GET", "arvados/v1/api_client_authorizations/"+key, nil, nil)
 151                 secret = aca.APIToken
 152         } else {
 153                 // Access key and secret key are both an entire
 154                 // Arvados token or OIDC access token.
 155                 ctx := arvados.ContextWithAuthorization(r.Context(), "Bearer "+key)
 156                 err = client.RequestAndDecodeContext(ctx, &aca, "GET", "arvados/v1/api_client_authorizations/current", nil, nil)
 157                 secret = key
 158         }
 159         if err != nil {
 160                 ctxlog.FromContext(r.Context()).WithError(err).WithField("UUID", key).Info("token lookup failed")
 161                 return "", errors.New("invalid access key")
 162         }
 163         stringToSign, err := s3stringToSign(s3SignAlgorithm, scope, signedHeaders, r)
 164         if err != nil {
 165                 return "", err
 166         }
 167         expect, err := s3signature(secret, scope, signedHeaders, stringToSign)
 168         if err != nil {
 169                 return "", err
 170         } else if expect != signature {
 171                 return "", fmt.Errorf("signature does not match (scope %q signedHeaders %q stringToSign %q)", scope, signedHeaders, stringToSign)
 172         }
 173         return secret, nil
 174 }
 175
 176 func s3ErrorResponse(w http.ResponseWriter, s3code string, message string, resource string, code int) {
 177         w.Header().Set("Content-Type", "application/xml")
 178         w.Header().Set("X-Content-Type-Options", "nosniff")
 179         w.WriteHeader(code)
 180         fmt.Fprintf(w, `<?xml version="1.0" encoding="UTF-8"?>
 181 <Error>
 182   <Code>%v</Code>
 183   <Message>%v</Message>
 184   <Resource>%v</Resource>
 185   <RequestId></RequestId>
 186 </Error>`, code, message, resource)
 187 }
 188
 189 var NoSuchKey = "NoSuchKey"
 190 var NoSuchBucket = "NoSuchBucket"
 191 var InvalidArgument = "InvalidArgument"
 192 var InternalError = "InternalError"
 193 var UnauthorizedAccess = "UnauthorizedAccess"
 194 var InvalidRequest = "InvalidRequest"
 195 var SignatureDoesNotMatch = "SignatureDoesNotMatch"
 196
 197 // serveS3 handles r and returns true if r is a request from an S3
 198 // client, otherwise it returns false.
 199 func (h *handler) serveS3(w http.ResponseWriter, r *http.Request) bool {
 200         var token string
 201         if auth := r.Header.Get("Authorization"); strings.HasPrefix(auth, "AWS ") {
 202                 split := strings.SplitN(auth[4:], ":", 2)
 203                 if len(split) < 2 {
 204                         s3ErrorResponse(w, InvalidRequest, "malformed Authorization header", r.URL.Path, http.StatusUnauthorized)
 205                         return true
 206                 }
 207                 token = split[0]
 208         } else if strings.HasPrefix(auth, s3SignAlgorithm+" ") {
 209                 t, err := h.checks3signature(r)
 210                 if err != nil {
 211                         s3ErrorResponse(w, SignatureDoesNotMatch, "signature verification failed: "+err.Error(), r.URL.Path, http.StatusForbidden)
 212                         return true
 213                 }
 214                 token = t
 215         } else {
 216                 return false
 217         }
 218
 219         _, kc, client, release, err := h.getClients(r.Header.Get("X-Request-Id"), token)
 220         if err != nil {
 221                 s3ErrorResponse(w, InternalError, "Pool failed: "+h.clientPool.Err().Error(), r.URL.Path, http.StatusInternalServerError)
 222                 return true
 223         }
 224         defer release()
 225
 226         fs := client.SiteFileSystem(kc)
 227         fs.ForwardSlashNameSubstitution(h.Config.cluster.Collections.ForwardSlashNameSubstitution)
 228
 229         objectNameGiven := strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 1
 230
 231         switch {
 232         case r.Method == http.MethodGet && !objectNameGiven:
 233                 // Path is "/{uuid}" or "/{uuid}/", has no object name
 234                 if _, ok := r.URL.Query()["versioning"]; ok {
 235                         // GetBucketVersioning
 236                         w.Header().Set("Content-Type", "application/xml")
 237                         io.WriteString(w, xml.Header)
 238                         fmt.Fprintln(w, `<VersioningConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"/>`)
 239                 } else {
 240                         // ListObjects
 241                         h.s3list(w, r, fs)
 242                 }
 243                 return true
 244         case r.Method == http.MethodGet || r.Method == http.MethodHead:
 245                 fspath := "/by_id" + r.URL.Path
 246                 fi, err := fs.Stat(fspath)
 247                 if r.Method == "HEAD" && !objectNameGiven {
 248                         // HeadBucket
 249                         if err == nil && fi.IsDir() {
 250                                 w.WriteHeader(http.StatusOK)
 251                         } else if os.IsNotExist(err) {
 252                                 s3ErrorResponse(w, NoSuchBucket, "The specified bucket does not exist.", r.URL.Path, http.StatusNotFound)
 253                         } else {
 254                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 255                         }
 256                         return true
 257                 }
 258                 if err == nil && fi.IsDir() && objectNameGiven && strings.HasSuffix(fspath, "/") && h.Config.cluster.Collections.S3FolderObjects {
 259                         w.Header().Set("Content-Type", "application/x-directory")
 260                         w.WriteHeader(http.StatusOK)
 261                         return true
 262                 }
 263                 if os.IsNotExist(err) ||
 264                         (err != nil && err.Error() == "not a directory") ||
 265                         (fi != nil && fi.IsDir()) {
 266                         s3ErrorResponse(w, NoSuchKey, "The specified key does not exist.", r.URL.Path, http.StatusNotFound)
 267                         return true
 268                 }
 269                 // shallow copy r, and change URL path
 270                 r := *r
 271                 r.URL.Path = fspath
 272                 http.FileServer(fs).ServeHTTP(w, &r)
 273                 return true
 274         case r.Method == http.MethodPut:
 275                 if !objectNameGiven {
 276                         s3ErrorResponse(w, InvalidArgument, "Missing object name in PUT request.", r.URL.Path, http.StatusBadRequest)
 277                         return true
 278                 }
 279                 fspath := "by_id" + r.URL.Path
 280                 var objectIsDir bool
 281                 if strings.HasSuffix(fspath, "/") {
 282                         if !h.Config.cluster.Collections.S3FolderObjects {
 283                                 s3ErrorResponse(w, InvalidArgument, "invalid object name: trailing slash", r.URL.Path, http.StatusBadRequest)
 284                                 return true
 285                         }
 286                         n, err := r.Body.Read(make([]byte, 1))
 287                         if err != nil && err != io.EOF {
 288                                 s3ErrorResponse(w, InternalError, fmt.Sprintf("error reading request body: %s", err), r.URL.Path, http.StatusInternalServerError)
 289                                 return true
 290                         } else if n > 0 {
 291                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless content is empty", r.URL.Path, http.StatusBadRequest)
 292                                 return true
 293                         } else if strings.SplitN(r.Header.Get("Content-Type"), ";", 2)[0] != "application/x-directory" {
 294                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless Content-Type is 'application/x-directory'", r.URL.Path, http.StatusBadRequest)
 295                                 return true
 296                         }
 297                         // Given PUT "foo/bar/", we'll use "foo/bar/."
 298                         // in the "ensure parents exist" block below,
 299                         // and then we'll be done.
 300                         fspath += "."
 301                         objectIsDir = true
 302                 }
 303                 fi, err := fs.Stat(fspath)
 304                 if err != nil && err.Error() == "not a directory" {
 305                         // requested foo/bar, but foo is a file
 306                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 307                         return true
 308                 }
 309                 if strings.HasSuffix(r.URL.Path, "/") && err == nil && !fi.IsDir() {
 310                         // requested foo/bar/, but foo/bar is a file
 311                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 312                         return true
 313                 }
 314                 // create missing parent/intermediate directories, if any
 315                 for i, c := range fspath {
 316                         if i > 0 && c == '/' {
 317                                 dir := fspath[:i]
 318                                 if strings.HasSuffix(dir, "/") {
 319                                         err = errors.New("invalid object name (consecutive '/' chars)")
 320                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 321                                         return true
 322                                 }
 323                                 err = fs.Mkdir(dir, 0755)
 324                                 if err == arvados.ErrInvalidArgument {
 325                                         // Cannot create a directory
 326                                         // here.
 327                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 328                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 329                                         return true
 330                                 } else if err != nil && !os.IsExist(err) {
 331                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 332                                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 333                                         return true
 334                                 }
 335                         }
 336                 }
 337                 if !objectIsDir {
 338                         f, err := fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 339                         if os.IsNotExist(err) {
 340                                 f, err = fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 341                         }
 342                         if err != nil {
 343                                 err = fmt.Errorf("open %q failed: %w", r.URL.Path, err)
 344                                 s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 345                                 return true
 346                         }
 347                         defer f.Close()
 348                         _, err = io.Copy(f, r.Body)
 349                         if err != nil {
 350                                 err = fmt.Errorf("write to %q failed: %w", r.URL.Path, err)
 351                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 352                                 return true
 353                         }
 354                         err = f.Close()
 355                         if err != nil {
 356                                 err = fmt.Errorf("write to %q failed: close: %w", r.URL.Path, err)
 357                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 358                                 return true
 359                         }
 360                 }
 361                 err = fs.Sync()
 362                 if err != nil {
 363                         err = fmt.Errorf("sync failed: %w", err)
 364                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 365                         return true
 366                 }
 367                 w.WriteHeader(http.StatusOK)
 368                 return true
 369         case r.Method == http.MethodDelete:
 370                 if !objectNameGiven || r.URL.Path == "/" {
 371                         s3ErrorResponse(w, InvalidArgument, "missing object name in DELETE request", r.URL.Path, http.StatusBadRequest)
 372                         return true
 373                 }
 374                 fspath := "by_id" + r.URL.Path
 375                 if strings.HasSuffix(fspath, "/") {
 376                         fspath = strings.TrimSuffix(fspath, "/")
 377                         fi, err := fs.Stat(fspath)
 378                         if os.IsNotExist(err) {
 379                                 w.WriteHeader(http.StatusNoContent)
 380                                 return true
 381                         } else if err != nil {
 382                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 383                                 return true
 384                         } else if !fi.IsDir() {
 385                                 // if "foo" exists and is a file, then
 386                                 // "foo/" doesn't exist, so we say
 387                                 // delete was successful.
 388                                 w.WriteHeader(http.StatusNoContent)
 389                                 return true
 390                         }
 391                 } else if fi, err := fs.Stat(fspath); err == nil && fi.IsDir() {
 392                         // if "foo" is a dir, it is visible via S3
 393                         // only as "foo/", not "foo" -- so we leave
 394                         // the dir alone and return 204 to indicate
 395                         // that "foo" does not exist.
 396                         w.WriteHeader(http.StatusNoContent)
 397                         return true
 398                 }
 399                 err = fs.Remove(fspath)
 400                 if os.IsNotExist(err) {
 401                         w.WriteHeader(http.StatusNoContent)
 402                         return true
 403                 }
 404                 if err != nil {
 405                         err = fmt.Errorf("rm failed: %w", err)
 406                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 407                         return true
 408                 }
 409                 err = fs.Sync()
 410                 if err != nil {
 411                         err = fmt.Errorf("sync failed: %w", err)
 412                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 413                         return true
 414                 }
 415                 w.WriteHeader(http.StatusNoContent)
 416                 return true
 417         default:
 418                 s3ErrorResponse(w, InvalidRequest, "method not allowed", r.URL.Path, http.StatusMethodNotAllowed)
 419
 420                 return true
 421         }
 422 }
 423
 424 // Call fn on the given path (directory) and its contents, in
 425 // lexicographic order.
 426 //
 427 // If isRoot==true and path is not a directory, return nil.
 428 //
 429 // If fn returns filepath.SkipDir when called on a directory, don't
 430 // descend into that directory.
 431 func walkFS(fs arvados.CustomFileSystem, path string, isRoot bool, fn func(path string, fi os.FileInfo) error) error {
 432         if isRoot {
 433                 fi, err := fs.Stat(path)
 434                 if os.IsNotExist(err) || (err == nil && !fi.IsDir()) {
 435                         return nil
 436                 } else if err != nil {
 437                         return err
 438                 }
 439                 err = fn(path, fi)
 440                 if err == filepath.SkipDir {
 441                         return nil
 442                 } else if err != nil {
 443                         return err
 444                 }
 445         }
 446         f, err := fs.Open(path)
 447         if os.IsNotExist(err) && isRoot {
 448                 return nil
 449         } else if err != nil {
 450                 return fmt.Errorf("open %q: %w", path, err)
 451         }
 452         defer f.Close()
 453         if path == "/" {
 454                 path = ""
 455         }
 456         fis, err := f.Readdir(-1)
 457         if err != nil {
 458                 return err
 459         }
 460         sort.Slice(fis, func(i, j int) bool { return fis[i].Name() < fis[j].Name() })
 461         for _, fi := range fis {
 462                 err = fn(path+"/"+fi.Name(), fi)
 463                 if err == filepath.SkipDir {
 464                         continue
 465                 } else if err != nil {
 466                         return err
 467                 }
 468                 if fi.IsDir() {
 469                         err = walkFS(fs, path+"/"+fi.Name(), false, fn)
 470                         if err != nil {
 471                                 return err
 472                         }
 473                 }
 474         }
 475         return nil
 476 }
 477
 478 var errDone = errors.New("done")
 479
 480 func (h *handler) s3list(w http.ResponseWriter, r *http.Request, fs arvados.CustomFileSystem) {
 481         var params struct {
 482                 bucket    string
 483                 delimiter string
 484                 marker    string
 485                 maxKeys   int
 486                 prefix    string
 487         }
 488         params.bucket = strings.SplitN(r.URL.Path[1:], "/", 2)[0]
 489         params.delimiter = r.FormValue("delimiter")
 490         params.marker = r.FormValue("marker")
 491         if mk, _ := strconv.ParseInt(r.FormValue("max-keys"), 10, 64); mk > 0 && mk < s3MaxKeys {
 492                 params.maxKeys = int(mk)
 493         } else {
 494                 params.maxKeys = s3MaxKeys
 495         }
 496         params.prefix = r.FormValue("prefix")
 497
 498         bucketdir := "by_id/" + params.bucket
 499         // walkpath is the directory (relative to bucketdir) we need
 500         // to walk: the innermost directory that is guaranteed to
 501         // contain all paths that have the requested prefix. Examples:
 502         // prefix "foo/bar"  => walkpath "foo"
 503         // prefix "foo/bar/" => walkpath "foo/bar"
 504         // prefix "foo"      => walkpath ""
 505         // prefix ""         => walkpath ""
 506         walkpath := params.prefix
 507         if cut := strings.LastIndex(walkpath, "/"); cut >= 0 {
 508                 walkpath = walkpath[:cut]
 509         } else {
 510                 walkpath = ""
 511         }
 512
 513         type commonPrefix struct {
 514                 Prefix string
 515         }
 516         type listResp struct {
 517                 XMLName string `xml:"http://s3.amazonaws.com/doc/2006-03-01/ ListBucketResult"`
 518                 s3.ListResp
 519                 // s3.ListResp marshals an empty tag when
 520                 // CommonPrefixes is nil, which confuses some clients.
 521                 // Fix by using this nested struct instead.
 522                 CommonPrefixes []commonPrefix
 523                 // Similarly, we need omitempty here, because an empty
 524                 // tag confuses some clients (e.g.,
 525                 // github.com/aws/aws-sdk-net never terminates its
 526                 // paging loop).
 527                 NextMarker string `xml:"NextMarker,omitempty"`
 528                 // ListObjectsV2 has a KeyCount response field.
 529                 KeyCount int
 530         }
 531         resp := listResp{
 532                 ListResp: s3.ListResp{
 533                         Name:      strings.SplitN(r.URL.Path[1:], "/", 2)[0],
 534                         Prefix:    params.prefix,
 535                         Delimiter: params.delimiter,
 536                         Marker:    params.marker,
 537                         MaxKeys:   params.maxKeys,
 538                 },
 539         }
 540         commonPrefixes := map[string]bool{}
 541         err := walkFS(fs, strings.TrimSuffix(bucketdir+"/"+walkpath, "/"), true, func(path string, fi os.FileInfo) error {
 542                 if path == bucketdir {
 543                         return nil
 544                 }
 545                 path = path[len(bucketdir)+1:]
 546                 filesize := fi.Size()
 547                 if fi.IsDir() {
 548                         path += "/"
 549                         filesize = 0
 550                 }
 551                 if len(path) <= len(params.prefix) {
 552                         if path > params.prefix[:len(path)] {
 553                                 // with prefix "foobar", walking "fooz" means we're done
 554                                 return errDone
 555                         }
 556                         if path < params.prefix[:len(path)] {
 557                                 // with prefix "foobar", walking "foobag" is pointless
 558                                 return filepath.SkipDir
 559                         }
 560                         if fi.IsDir() && !strings.HasPrefix(params.prefix+"/", path) {
 561                                 // with prefix "foo/bar", walking "fo"
 562                                 // is pointless (but walking "foo" or
 563                                 // "foo/bar" is necessary)
 564                                 return filepath.SkipDir
 565                         }
 566                         if len(path) < len(params.prefix) {
 567                                 // can't skip anything, and this entry
 568                                 // isn't in the results, so just
 569                                 // continue descent
 570                                 return nil
 571                         }
 572                 } else {
 573                         if path[:len(params.prefix)] > params.prefix {
 574                                 // with prefix "foobar", nothing we
 575                                 // see after "foozzz" is relevant
 576                                 return errDone
 577                         }
 578                 }
 579                 if path < params.marker || path < params.prefix {
 580                         return nil
 581                 }
 582                 if fi.IsDir() && !h.Config.cluster.Collections.S3FolderObjects {
 583                         // Note we don't add anything to
 584                         // commonPrefixes here even if delimiter is
 585                         // "/". We descend into the directory, and
 586                         // return a commonPrefix only if we end up
 587                         // finding a regular file inside it.
 588                         return nil
 589                 }
 590                 if params.delimiter != "" {
 591                         idx := strings.Index(path[len(params.prefix):], params.delimiter)
 592                         if idx >= 0 {
 593                                 // with prefix "foobar" and delimiter
 594                                 // "z", when we hit "foobar/baz", we
 595                                 // add "/baz" to commonPrefixes and
 596                                 // stop descending.
 597                                 commonPrefixes[path[:len(params.prefix)+idx+1]] = true
 598                                 return filepath.SkipDir
 599                         }
 600                 }
 601                 if len(resp.Contents)+len(commonPrefixes) >= params.maxKeys {
 602                         resp.IsTruncated = true
 603                         if params.delimiter != "" {
 604                                 resp.NextMarker = path
 605                         }
 606                         return errDone
 607                 }
 608                 resp.Contents = append(resp.Contents, s3.Key{
 609                         Key:          path,
 610                         LastModified: fi.ModTime().UTC().Format("2006-01-02T15:04:05.999") + "Z",
 611                         Size:         filesize,
 612                 })
 613                 return nil
 614         })
 615         if err != nil && err != errDone {
 616                 http.Error(w, err.Error(), http.StatusInternalServerError)
 617                 return
 618         }
 619         if params.delimiter != "" {
 620                 resp.CommonPrefixes = make([]commonPrefix, 0, len(commonPrefixes))
 621                 for prefix := range commonPrefixes {
 622                         resp.CommonPrefixes = append(resp.CommonPrefixes, commonPrefix{prefix})
 623                 }
 624                 sort.Slice(resp.CommonPrefixes, func(i, j int) bool { return resp.CommonPrefixes[i].Prefix < resp.CommonPrefixes[j].Prefix })
 625         }
 626         resp.KeyCount = len(resp.Contents)
 627         w.Header().Set("Content-Type", "application/xml")
 628         io.WriteString(w, xml.Header)
 629         if err := xml.NewEncoder(w).Encode(resp); err != nil {
 630                 ctxlog.FromContext(r.Context()).WithError(err).Error("error writing xml response")
 631         }
 632 }